Examples of projection objectives for microlithography are disclosed in U.S. Pat. No. 6,266,389 B1, in US 2005/0134980 A1, in US 2007/0195317 A1, in US 2007/0058269 A1, in US 2007/0223112 A, in U.S. Pat. Nos. 6,396,067 B1, 6,361,176 B1 and 6,666,560 B2.